US3267709A

US3267709A - Method and apparatus for controlling temperature of the workpiece during rolling

Info

Publication number: US3267709A
Application number: US302024A
Authority: US
Inventors: O'brien Jeremiah Wagner
Original assignee: United Engineering and Foundry Co
Current assignee: United Engineering and Foundry Co
Priority date: 1962-08-24
Filing date: 1963-08-14
Publication date: 1966-08-23
Anticipated expiration: 1983-08-23
Also published as: GB977485A; BE636442A; ES291037A1; DE1293114B

Description

J. w. O'BRIEN 3,267,709 METHOD AND APPARATUS FOR CONTROLLING TEMPERATURE Aug. 23, 1966 OF THE WORKPIECE DURING ROLLING 2 Sheets-Sheet 1 Filed Aug. 14, 1963 N y m E m1 m @M N HN R mo m m E. mm H Q M M Q Q J 7,

nited States This invention relates to a method of and apparatus for rolling metallic elongated workpieces and, more particularly, to a hot strip rolling mill incorporating a continuous tandemly arranged finishing train.

One of the long-standing and serious problems connected with the operation of a continuous or semi-continuous hot strip mill has reference to the objectionable effects, such as, gauge and metallurgical variations, caused by the inherent differential temperature condition that exists between different lengthwise portions of the strip, particularly, when the strip is being rolled in the finishing train. Since the speed of this train is maintained constant, the rearward portions of the strip are exposed progressively longerto the atmosphere than the forward portions thereof. This condition thus results in the strip having a differential temperature from end to end which may be as much as 150 F.

Another problem has reference to the difiiculty in maintaining the desired temperature level of the strip during the rolling thereof in the finishing train which is desirable for metallurgical reasons. The more difficult of these two problems is presented by the variation in the end-toencl temperature of the strip, since the temperature level condition can be controlled to an appreciable extent by an appropriate adjustment of the slab furnaces, the use of a delay table on which the strip is held prior to rolling until the proper temperature level is obtained and by the employment of water sprays. Notwithstanding, there still exists a need for an improved manner of obtaining finer temperature level control. That such temperature differential be kept within a well defined and low limit and the strip temperature level be maintained at a predetermined range is of paramount importance if the optimum metallurgy and gauge tolerance of the strip is to be consistently obtained.

In the past several attempts were made to control the differential temperature condition of the strip. One was to utilize controlled water sprays which were located either immediately before the first finishing stand or between one or more of the stands of the train. However, in more recently constructed mills the principal method employed is to roll the entire strip at a higher constant speed than was previously done. In this manner the total rolling time for reducing the strip is reduced and, as a result, so is the temperature differential, since the rearward end of the strip at the entry side of the train is exposed to the atmosphere for a shorter period of time. While these attempts were beneficial to some degree, the success thereof was limited in nature.

As to the procedure of rolling the strip at a higher constant speed, the maximum speed obtainable, when rolling the front portion of the strip, was limited to the speed at which the strip could be successfully issued onto the runout table without it valoplaning, i.e., tends to lift off the table due to the air current, and its leading end entered into the coiler. Moreover, the previous attempts to correct for the differential temperature condition fell short of meeting the demands of the modern continuous and semi-continuous hot strip mills. These mills, in-

atent ICC augurated the practice of rolling much larger slabs than previously rolled, hence the length of the strips greatly increased over previously rolled strips, and consequently, the differential temperature condition also substantially increased over what was previously experienced.

The present invention not only overcomes the abovementioned shortcomings of the previous means and methods of temperature control of the strip in the finishing train of a hot strip mill, but of even more significance, it successfully meets the demands of the modern strip mills wherein very long coils are produced.

According to the present invention, there is provided a method of and apparatus for controlling the hot rolling of strip wherein the end-to-end temperature differential of the strip during rolling in the finishing train can be greatly reduced and, if necessary, substantially totally eliminated; and, wherein, if desired, the temperature level of the strip during the rolling operation can be automatically and narrowly controlled.

To accomplish these objectives, in one form, the finishing train is operated so that the speed of each stand thereof is proportionately increased in unison as the strip is rolled, whereby the rearward portions of the strip are introduced into the first mill stand at a greater velocity than the forward portions thereof. The speed ratio of the stands, however, will not necessarily be disturbed. As a result, the end-to-end temperature differential of the strip may be substantially decreased and a substantial constant temperature condition obtained throughout the entire strip. As more fully explained hereinafter, the required increase in the delivery velocity of the strip at a given point on the strip necessary to obtain the desired temperature at that point will equal the sum of the temperature losses incident to radiation and conduction of an earlier point on the strip multiplied by the delivery velocity of the earlier point, which product is divided by the sum of the temperature losses incident to radiation and conduction of the earlier point subtracted from the difference in temperature between the given and earlier points as these points enter the train.

In one form of the invention the speed of the finishing train, runout table and strip coiler will be adjusted in unison, in which regard the speeds of these units will be accelerated immediately after the strip has been started on the mandrel of the coiler. In still another case the speeds of the train can be progressively and continuously increased as soon as the material is in the train and the speeds of the other units will be raised to match that of the train as the material passes to them, the initial speed of the train being within the limits that assure successful conveyance of the strip over the runout table and commencement of the coiling operation.

It is another feature of this invention to employ a device that will either determine the temperature of the strip during the rolling operation or the temperature differential between two or more portions thereof, which information is related to a controller of the motors of the train which will adjust the speed thereof to obtain the desired temperature condition. If desired, the speed can also be adjusted to obtain a refinement of the temperature level of the strip over a substantial portion thereof.

The present invention will be better understood when the following description is read with the accompanying drawings of which:

FIGURE 1 is a schematic elevational view of a finishing train of a hot strip mill, illustrating also the runout table and the strip downcoilers thereof;

FIGURE 2 is a schematic view of one of the mills shown in FIGURE 1, illustrating the roll pass adjustment mechanism thereof;

FIGURE 3 is an electrical diagram of the control employed in operating the mill arrangement illustrated in FEGURE 1 to practice the present invention; and

FIGURE 4 is a graph illustrating the result of varying the speeds or" the strip in relationship to the length of the strip being processed.

With reference to FIGURE 1 of the drawings, there is illustrated for processing a strip S, the finishing end of a continuous hot strip rnill, including a 4-high sixstand finishing train consisting of stands l1, l2, l3, l4, and 15, a runout table 17 and two downcoilers l8 and 19.

The motors 2i are shown for the stands, each having a tachometer 22, the tachometer of the stand 16 being shown connected to its motor 21 by a train of gears 23 to which there is also connected a pilot generator 25. The rollers of the runout table 17 are driven by motors 26, two of which only are shown. Above the table 17 there are provided a number of strip cooling sprays 27. The downcoilers lo and 19 are driven by motors 23, each having a control 29 which is electrically connected to the pilot generator 25 of the last stand is of the finishing train.

FIGURE 1 also diagrammatically illustrates three temperature detecting devices, such as

pyrometers

3b, 31 and 32, the pyrometer 35 being arranged at the entry side of the train, the pyrometer 31 on the exit side thereof and the pyrometer 32 on the entry side of downcoiler 18. In still referring to FIGURE 1, an X-ray strip thickness gauge 33 is arranged at the exit side of the mill stand 16.

With reference to FIGURE 2 which shows a diagrammatic arrangement for adjusting the pass of one of the stands 1146, there is provided a pair of working rolls 34- between which the strip S passes, each working roll being supported by backing-up rolls 35. One of a pair of bearing-checks 36 is also shown for the upper backing-up roll which is engaged by the lower end of the mill screw 37. At the upper end of the mill screw 37, there is secured thereto a gear wheel 33 which is rotated by a worm 3-9, the worm being connected by gearing 41 to a piston cylinder assembly 42 and an electrical motor 43. The motor and piston cylinder assembly serve as a low-speed, high torque and low torque, high-speed prime movers, respectively, the two working together to provide a strip guage control arrangement.

In view of the fact that the increase in speed of the finishing train may under certain conditions influence detrimentally the guage of the strip, it is to be understood that one or more of the stands may be provided with an automatic gauge control device as previously noted and as illustrated in FlGURE 2. This variation in gauge, however, should be less than the gauge variation that would otherwise be caus d by the end-to-end temperature differential condition. While a pass adjustment to obtain gauge control is described, it will be apreciated that in combination therewith or separate therefrom variable controllable tension on the strip as it passes etween two or more of the adjacent stands can be employed.

The rolling equipment illustrated in FIGURE 1 is, of course, well known as exemplified by chapter 33 in the making, shaping, heat treating of steel published by the US. Steel Corporation, 7th edition, and the material referred to in the bibliography thereof The mill screwdown arrangement shown in FIGURE 2 is more fully described in US. patent application No. 3,104,567, issued to M. P. Sieger on September 24, 1963 entitled Rolling Mill Screwdown Apparatus. It will be appreciated that other well-known pass adjusting devices can be employed, such as, illustrated in US. Patent No. 2,961,901 that was issued to S. Wheeler on November 29, 1960 entitled Automatic Control for Adjusting Rolling Mills. The connection between the strip thickness X-ray gauge 33 and the piston cylinder asof the scrcwdown can follow the arrangement in FIGURE 7 of the aforesaid Wheeler patsembly illustrated cut.

The

motors

21, 26 and 23, provide for the finishing train, the runout table and the downcoilers l8 and respectively, are controlled in a well-known manner so that their speeds can be proportionately varied in unison. Moreover, the strip cooling device employed with the runout table 14 is constructed also in a Wellwn manner so as to vary its output in accordance with the change in speed of the train. In this manner, as the speeds increase, the discharge from the strip cooling system will increase proportionately.

While it will be appreciated. that the speed of the finishing train can be adjusted manually or at a given time in relationship to passage of the strip through the mill, this adjustment can be preferably effected by automatically adjusting the speeds of the stands pursuant to the continuous changing temperature condition of the strip being fed through the finishing train. ()ne manner of doing this would be to measure the temperature of the strip as it passes from the last stand of the finishing train and increase the speeds of the stands to the extent necessary to reduce the differential temperature to permissible limits or, if desired, to substantially eliminote it. Another manner of adjusting the mill speeds to correct for the temperature differential would be to utilize a computer to which would be continuously fed either theoretical or empirical relationships of the various factors involved as the temperature changes of the strip during the rolling process. A still further manner would be to op a program system based on past performln this ngard FIGURE 3 illustrates the principal components of the computer system in which there is illustrated diagrammatically the pyrometers 3%, Bl and 32.

A volta e signal from pyrometer which is proportional output signal from the amplifier =5 is fed to an operational ampli which also receives a signal The relay input which by the coilcr motor current when the strip 1' the coiler permits amplifier begins wrap! ing around to operate and ampnry the input voltage from the amplifier 45 and feed a signal to a stunning amplifier 57 which, in turn, feeds the main drive control current to start the finishing train acceleration and correct for temperature variations detected by the delivery pyrometer 31.

The amplifier 5-5 has within itself a bias which is in effect an acceleration rate r ,astrnent. The voltage output of the amplifier is therefore modified for a certain accelerating rate. This output, in turn, modified the output of amplifier 4'7 to give a certain accelerating rate to the finishing train which will limit the accelerating rate established by the speed of operation of a motoroperated rheostat, not shown.

The voltage output of the summing amplifier 4-5 feeds another summing amplifier 51. This amplifier receives three other voltage s nals, a voltage signal rep resenting the temperature or the strip at the entry end of the mill as obtained by the pyrorneter 31' a voltage representing the temperature of the strip at the delivery end of the mill as obtained by the pyrometer 31 and a manual preset voltage signal. The voltage output signal from the amplifier will represent the difference between the signal from the output amplifier 45 and the sum of the signals from the pyrometers 3-53 and 31. This signal will then be sent on to an amplifier which, in turn, feeds a voltage signal to the amplifier :7.

also

The voltage output from the coiler pyrometer 32 is fed to a summing amplifier 48. The amplifier 48 receives a second voltage signal from the tachometer 22, it being noted that the tachometer feeds a voltage signal also to the amplifier 47, the latter signal representing delivery speed of the finishing mill train. The output voltage signal represents the difference between the voltage input from the pyrometer 32 and the tachometer voltage input. This signal will have polarity and is fed to the control of the spray valve section and the cooling water spray valves to increase or decrease the amount of cooling water.

To better understand the functions of the above circuit, the various inputs and outputs of the amplifiers will be expressed in terms of Equation 8 appearing in column 8 as follows:

(ATCp1+ ATRP, Vdd.P,

The operational amplifier 47 receives a voltage signal ATC +TR from the amplifier 46, a voltage signal (ATC +ATR )-(Tel1t. Tent. from the

amplifiers

51 and 53 and a voltage signal VdeL from the tachometer 22 and solves the aforesaid equation to produce a voltage signal representing the desired delivery speed of the mill to correct for a temperature differential existing between a first point from the strip (P and a second point (P The various elements making up the aforesaid computer system are of well-known construction, in which the various amplifiers are of the type discussed under operational amplifiers in G. A. Korn et al. Electronic Analog Computers, Second edition, 1956, McGraw-Hill Book Company, Inc.

Returning to the operational amplifier 47, it will be noted in FIGURE 3 that it feeds a signal to an operational amplifier 58 which feeds to a motor speed control 59; the operational amplifier 58 also receives signals from rectifiers 61 and 62, the rectfiiers producing signals which are also received by an operational amplifier 63 which is electrically tied in with a pilot servo-system 64 which feeds a signal to an amplifier 65 which, in turn, feeds a signal to a regulator 65. In the circuit of the control 59 there is illustrated one of the motors 21 of the train along with the tachometer 22, in which connection it will be noted that the tachometer 22 is connected to the operational amplifier 47. The motor control circuit which may be defined as those units between and including the operational amplifier 47 and the motor control 59 are quite well known as illustrated in FIGURE 2 of Iron and Steel Engineers yearbook 1961, page 426 entitled Hot Strip Mill Electrical System, Design Trends, by W. M. Krummel and for this reason a more detailed discussion of the circuit will not be given.

With respect to the matter of operating the train to obtain temperature control which is graphically illustrated in FIGURE 4, it will be seen that a signal from the delivery pyrometer 31 through the amplifiers 45, 46, 47 and 58 will initiate the operation of the control 59, which will then regulate the speed of the motors 21 whereby the temperature level of the strip will be brought to a predetermined value as set by the manual adjustment of the operational amplifier 51. Moreover, it will be seen from FIGURE 3 that the signals of the

pyrometers

30 and 31 will be integrated in a manner to produce a signal received by the operational amplifier 47, which through the amplifier 58, will dictate to the control 59 to effect a motor speed change commensurate with the differential detected in the temperature of the strip passing under the

pyrometers

30 and 31.

It will be appreciated that the

motors

26 and 28 are also tied in to the control 59 and these speeds will be regulated with the speeds of the motors 21 of the train.

To better understand the behavior and the herein-disclosed method of controlling the temperature of the strip during the rolling operation in a finishing train the following analysis is given, let:

P represent a point at the leading end of the strip;

P represent some other point along the strip;

Temt represent the entering temperature of the strip at the first finishing stand of point P TdeL represent the delivery temperature of the strip at the last finishing stand of point P Tent. represent the entering temperature of the strip at the first finishing stand of point P TdeL represent the delivery temperature of the strip at the last finishing stand of point P ATH ATH represent the temperature increase of the strip at points P and P in the finishing train due to heat input by the work of reduction;

ATC ATC represent the temperature decrease of the strip at points P and P in the finishing train due to conduction losses between the rolls and strip;

ATR ATR represent the temperature decrease as points P and P passed through the finishing train due to radiation losses;

VdeL VcleL represent the velocity of points P and P as they leave the last stand.

In solving for the delivery temperature of point P we have:

TdeL Tent. +ATH -ATC -ATR (1) In solving for the delivery temperature of point P we have:

TdeL :Tent. .,-l-ATH ATC .,ATR (2) Therefore, in order to obtain substantial uniformity in the temperature condition as the various points along the length of the strip issue from the last stand, the temperature of the points must be made to be equal to one another; therefore we make:

TdeL =TdeL 3 Inasmuch as the strip temperature increase due to work of reduction of the metal is constant regardless of velocities for any one schedule of reductions, except for a small secondary effect, we have:

ATHP1=ATHP2 4 Then if we subtract Equation 2 from Equation 1 and simplify, we have the resulting equation:

Tent. -Tent. (ATC -l-ATR PZ+ATRP2) By fulfilling the conditions of Equation 5 the temperature at points P and P will be the same as they leave the last finishing stand. By the same token, other points along the length of the strip, such as, P P P P could be maintained at the same temperature.

If the difference on the right-hand side of Equation 5 does not equal the difference on the left-hand side and, consequently does not fulfill the conditions required for equal finishing temperature, then it is possible to alter the values of (ATC -1-ATR by changing the speed of a finishing train, it follows that the difference between the expression on the right-hand side of the Equation 5 can be made to equal the difference between the expression on the left-hand side thereof. For example, by increasing the speed of the finishing train, the time in which a given portion of the strip passes between the rolls of the stand is reduced and, consequently, the conduction losses are reduced since the portion is in contact with the rolls for a shorter length of time. Similarly, an increase in speed will reduce the time of exposure for a given portion of the strip as it passes between the stands of the train and, consequently, the radiation losses are reduced at these areas.

9 Therefore, since the losses due to conduction and radiation are functions of the velocities, l del and VdeL for the points P and P this can be represented algebraically as:

Vdcl .p

In substituting in Equation (5), we have this expression:

T'GHLP1 T871145 (A TO -l A TRP1)"*(ATCP1 was,

Vdel

The relationship of velocities in Equation (8) is substantially correct, except for small secondary effects. From the above analysis it is evident that the temperature of the strip can be made substantially constant by varying the speed of the finishing train in the relationships indicated.

A brief description of one method of operating the illustrated mill in accordance with the present invention will now be given. As the strip issues from the last roughing stand, not shown, it will be received by the delay table, not shown; Whether or not the strip is held on the delay table to reduce its temperature to approximately the desired temperature level for rolling will depend upon the temperature condition of the strip. In any event should it be desired to either raise or lower the temperature level, the speeds of the respective stands 11-16 of the finishing train can be adjusted to obtain a refinement of the temperature level and maintain the level over a substantial portion of the strip, it being appreciated that this temperature adjustment is accomplished as previously explained in connection with the obtaining of uniform end-to-end temperature of the strip. As the strip is fed into the finishing train, the initial speed thereof as well as the speed of the runout table 17 will be maintained low enough to assure that the leading end of the strip will be successfully conveyed over the table and started on the mandrel of one of the coilers l8 and I This speed may vary from 1300 f.p.m. to slightly more than 2400 f.p.rn., depending upon the characteristics of the strip being rolled. The maximum speed range of the train may be as high as 3800 f.p.m. Of course, in a mill arrangement wherein the coilers were arranged immediately adjacent the last stand, higher initial speeds could be obtained;

7 Let it be assumed that the desired rolling temperature of the strip is about 1650 F. and that a portion of the front end leaving the mill is determined to be 1700 F. as detected by the delivery pyrometer 31. In this event, as previously noted, the detected temperature being different from the preselected temperature, as fed into the operational amplifier 51 by the manual control, will cause a signal to be produced and sent to the operational amplifier 47 which, in turn, will be fed to the operational amplifier 58 and, hence, to the control 59 which will cause a decrease in the speeds of the motors 21 of the train until the temperature reading of the strip leaving the finishing train is approximately 1600 F. The motors 26 of the runout table and the motors 28 of the particular coilers 18 and 19 that are being employed to receive a strip will also be correspondingly decelerated as well as the output of the sprays 27. In this instance the mill speed is adjusted to maintain a predetermined strip temperature level. Similarly, if the determined temperature is below the desired temperature, then in that event the speed of the train can be increased within the limit of effective conveyance of the strip to the coilers to increase the temperature of the strip leaving the last stand. A more inexact procedure would be to delay changing the speed of the train until the leading end of the strip is in the coiler.

Once the temperature level is obtained, the pyrometer system will signal the speed controller 5? to gradually and proportionately increase the speeds of the train, runi out table, coiler and output of the sprays 27 and, thus, to correct for the strip temperature differential when pass ing through the train so that the strip tWlll have an approximate, controlled temperature of about 165 0 F. Of course, the speed change need not be efieeted in a gradual manner, but could be accomplished at timed intervals or in one step. If the difference in speedbetween the front portion of the strip and the remainder thereof is great enough, a reversal of the initial temperature condition may be obtained, so that the rearward end of the strip will be hotter than the forward end thereof as it emerges from the last finishing stand. This condition is a result of the fact that at very high speeds the rate at which heat is introduced into the metal increases while the losses decrease, both to a very considerable extent.

It will be appreciated that, while only one pyrometer located at the delivery side of the train need only be employed, there would be some delay or transport time between the time the temperature losses occur and their recognition by the delivery temperature control. This, of necessity, will mean that the temperature control will not be too exact, but will still work within a narrow range. It will be further appreciated that a more exact control will be achieved by employing the pyrometer 30 ahead of the finishing stands to predict the required correction and, in this case, the delivery pyrometer will monitor the magnitude of the output signal from the entry pyrometer.

As mentioned previously, accompanying the progresive speed increase of the finishing train, if desired, will be a corresponding gauge correction to ofifset the efiect that the increase in speed may have on the gauge of the strip.

It can, therefore, be seen that the means and method herein disclosed provide for obtaining a substantial constant temperature between each portion of the strip as it passes a given point in the finishing train of a hot strip mill and, in addition, if desired, the refinement of the temperature level of a substantial portion of the strip. Moreover, an incident to the employment of this invention is that the productivity of the mill will be substantially increased.

It will be appreciated that the invention herein disclosed may be applied to any continuous rolling operation both ferrous and nonferrous, such as, for example, in the hot rolling of aluminum strip and in the hot rolling of ferrous and non-ferrous rods, bars, etc.

In accordance with the provisions of the patent statutes, 1 have explained the principle and operation of my invention and have illustrated and described what I consider to represent the best embodiment thereof, However, I desire to have it understood that Within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

It, In a method of rolling hot elongated workpieces, such as strip, in a train of rolling mills for reducing the thickness of the workpieces, wherein a temperature differential exists between lengthwise portions of the workpieces, comprising the steps of:

detecting a difference in temperature between two lengthwise portions of the strip,

determining the amount of said differences, and

adjusting the speed of the train commensurate with said amount to reduce said temperature difference by reducing the conduction and radiation losses of the portion of the strip having the lower temperature as it passes through the train.

2. In a method of rolling hot elongated workpieces,

such as strip, according to claim 1,

including the additional step of measuring the thickness of the strip as it is issued from the train,

determining the amount of variation in thickness from a desired thickness, and

changing the reduction taken in the train to obtain the desired thickness.

3. In a method of rolling elongated workpieces, such as strip, according to claim 2,

(A TC A TR VdeL ATCP, ATRp1)(Tent.p, Tent wherein:

P represents a point at the leading edge of the strip;

P represents some other point along the strip;

Tent represent the entering temperature of the strip at the first stand of point P Ta eL represent the delivery temperature of the strip at the last finishing stand of point P T emfl represent the entering temperature of the strip at the first finishing stand of point P TdeL represent the delivery temperature of the strip at the last finish-ing stand of point P ATH ATH represent the temperature increase of the strip at points P and P in the finishing train due to heat input by the work of reduction;

ATC ATC represents the temperature decrease of the strip at points P and P in the finishing train due to conduction losses between the rolls and strip;

ATR ATR represent the temperature decrease as points P and P passed through the finishing trains due to radiation losses; and

Va'eL VdeL represent the velocity of points P and P as they leave the last stand.

4. In a method of rolling hot elongated workpieces, such as strip, in a train of rolling mills for reducing the thickness of the workpieces, wherein a temperature differential exists between lengthwise portions of the workpieces, comprising the steps of:

obtainin ga signal representative of the amount of temperature differential between two portions of the strip, and

adjusting the speed of the train to reduce the temperature differential.

5. In a method of rolling, according to claim 4, wherein the strip is coiled after it has been rolled and strip cooling means is provided for cooling the strip after it leaves the train and prior to coiling,

the additional step of varying the coolingefiect commensurate with the adjustment of the speed of the train.

6. In a method of rolling hot elongated workpieces, such as strip, according to claim 4, including means for coiling the strip after rolling,

the additional steps of maintaining the speed of the train during passage of the leading end of the strip and prior to coiling thereof at a base speed below the maximum speed at which the leading end can be conveyed to the means for coiling the strip, and

increasing speed of the train from the base speed at a rate that does not exceed the maximum speed at which the leading end of the strip can be conveyed to the means for coiling the strip to reduce the temperature difference in the leading end of the strip.

7. In a hot rolling mill train consisting of a number of stands for processing strip,

means for driving the train at a variable speed,

means for generating a first signal representative of a desired temperature of strip during rolling,

means for generating a second signal representative of the degree of difference of the actual temperature of the strip at a given point and the desired temperature thereof, and

means for varying the speed of the train to reduce temperature losses while passing through the train, thereby reducing the temperature differential between the desired actual temperatures.

8. In a hot rolling mill, according to claim 7, including a means for cooling the strip after it issues from the train but prior to it being coiled, and

means for varying the cooling effect of the cooling means commensurate with the varying speed of the train.

9. In a hot rolling mill train consisting of a number of stands for processing strip,

means for driving the train at a variable speed,

means for determining the temperature of a first and second point on the strip,

means for determining the differences in temperature between said two points,

means for determining the speed of the strip of said first point, and

means controlled by said determined temperature difference and speed to adjust the speed of the train to reduce the temperature losses incident to radiation and conduction of said second point, thereby reducing the temperature differential between the first and second points.

10. In a hot rolling mill train, consisting of a number of stands for processing strip,

motors for driving the stands at variable speeds,

means for determining the speed of at least one of the stands,

means for determining the temperature of the strip at two different longitudinal spaced-apart points on the strip,

means for producing a signal representative of the difference in temperatures between said two points,

a speed controller, responsive to said signal and to said speed of said one stand, connected to said motors to adjust the speeds thereof to reduce the temperature losses of the strip passing through the train, whereby the difference in temperature between said two points will be reduced.

11. In a hot rolling mill train, according to claim 10,

wherein the adjusted speed of the stands is determined by the following formula:

wherein:

P represents a point at the leading edge of the strip;

P represents some other point along the strip;

Tent represents the entering temperature of the strip at the first finishing stand of point P TdeL represents the delivery temperature of the strip at the last finishing stand of point P TenL represents the entering temperature of the strip at the first finish-ing stand of point P TdeL represents the delivery temperature of the strip at the last finishing stand of point P ATH ATH represent the temperature increase of the strip at points P and P in the finishing train due to heat input by the work of reduction;

1 1 ATR ATR represent the temperature decrease as points P and P pass through the finishing train due to radiation losses; VdeL Vdeln; representthe velecity of points P and P; as they leave the last stand.

12. In a hot rolling mill train, according to claim 10, wherein said means for determining the temperature comprise pyrorneters located at the entry and delivery sides of the train.

References Cited by the Examiner UNITED STATES PATENTS Munker 729 Slarnar 72--9 Bar-nitz et a1. 80-351 Ludbrook et a1. 729

CHARLES W. LANHAM, Primary Examiner.

C. H. HITTSON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3, 267, 709 August 23, 1966 Jeremiah Wagner O'Brien It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 63, for "the making, shaping, heat treating of steel" read The Making, Shaping, Heat Treating of Steel column 4, line 4, for "provide" read provided column 5, lines 18 to 20, the formula should appear as shown below instead of as in the patent:

(ATC 1+ATR l) v dele l V del 2 (ATC ATR (T t T t en en 1 1 1 2 line 21 for "ATC +TR read ATC +ATR line 28 1 1 1 1 for (P read (P column 7, lines 5, 6 and 7, the formula should appear as shown below instead of as in the patent:

(ATC +ATR (ATC +ATR )Vdel a Vdel.p2

lines 18 to 20, the formula should appear as shown below instead of as in the patent:

ATC +ATR Vdel. 1 1 1 V del.

2 ATC +ATR Tent. -Tent column 9 line 9 for "as it is i d" ead as it issues line 28, for "at the first stand of point P read at the first finishing stand of point P line 51, for

"obtainin ga" read obtaining a column 10, line 13, after "disired" insert and column 10,

lines

64 and 65,

strike out "Tdel. represents the delivery temperature of l the strip at the last finishing stand of point P lines 68 and 69, strike out "TdeL 2 represents the delivery temperature of the strip at the last finishing stand of point P lines 7O, 71, and 72, strike out "ATH ATH represents the temperature increase of the strip at points P and P in the finishing train due to heat input by the work of reduction;"; line 73, strike out ",ATC same line 73, for "represent" read represents line 74, for "points" read point same line 74, strike out "and P column 11, line 1, strike out QATR Z"; same line 1, for "represent" read represents line 2, for "points read point same line 2, strike out "and P same line 2, for "pass" read passes Signed and sealed this 12th day of September 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J, BRENNER Attesting Officer Commissioner of Patents

Claims

1. IN A METHOD OF ROLLING HOT ELONGATED WORKPIECES, SUCH AS STRIP, IN A TRAIN OF ROLLING MILLS FOR REDUCING THE THICKNESS OF THE WORKPIECES, WHEREIN A TEMPERATURE DIFFERENTIAL EXISTS BETWEEN LENGTHWISE PORTIONS OF THE WORKPIECES, COMPRISING THE STEPS OF: DETECTING A DIFFERENCE IN TEMPERATURE BETWEEN TWO LENGTHWISE PORTIONS OF THE STRIP, DETERMINING THE AMOUNT OF SAID DIFFERENCES, AND ADJUSTING THE SPEED OF THE TRAIN COMMENSURATE WITH SAID AMOUNT TO REDUCE SAID TEMPERATURE DIFFERENCE BY REDUCING THE CONDUCTION AND RADIATION LOSSES OF THE PORTION OF THE STRIP HAVING THE LOWER TEMPERATURE AS IT PASSES THROUGH THE TRAIN.